Immunogenicity and safety of inactivated quadrivalent and trivalent influenza vaccines in children 18-47 months of age.

Background: Because inactivated trivalent influenza vaccines (TIVs) contain 1 influenza B strain, whereas 2 lineages may co-circulate, B lineage mismatch is frequent. We assessed an inactivated quadrivalent influenza vaccine (QIV) containing both B lineages versus TIV in young children.

Methods: Children aged 18-47 months who had received 2 doses of TIV in a study during the previous season (primed cohort, n = 192) were randomized 1:1 to receive 1 dose of TIV or QIV, and a further 407 children (unprimed cohort) were randomized 1:1 to receive 2 doses of TIV or QIV 28 days apart. Immunogenicity was assessed by hemagglutination-inhibition (HI) prevaccination and 28 days after each vaccination. Immunogenic non-inferiority QIV versus TIV for shared strains, and superiority against the alternate-lineage B strain were based on HI geometric mean titers (pooled analyses of primed and half of unprimed cohort with Day 56 immunogenicity assessment). Solicited and unsolicited adverse events were assessed during each 7- and 28-day postvaccination period, respectively (NCT00985790).

Results: Non-inferiority for shared strains and superiority for the alternate-lineage B strain unique to QIV was demonstrated for QIV versus TIV. QIV was immunogenic against all 4 vaccine strains and 87.0%, 88.6%, 69.8% and 97.9% of children had postvaccination titers of ≥ 1:40 against A/H1N1, A/H3N2, B/Victoria and B/Yamagata, respectively. Reactogenicity and safety of QIV was consistent with TIV.

Conclusions: QIV provided superior immunogenicity for the alternate-lineage B strain compared with TIV without interfering with immune responses to shared strains. Further studies are warranted to assess QIVs in children and to establish the clinical benefits of QIV versus TIV.